This invention relates to a simple, quantitative method for isolating and concentrating water soluble, polyacrylic acids from dilute aqueous systems containing polyacrylic acids and the other soluble ionic materials. More particularly, the invention relates to a method for selectively adsorbing and concentrating low concentrations of ionization suppressed polyacrylic acid, polymethacrylic acid, mixtures and copolymers thereof (hereinafter defined as polyacrylic acids) from aqueous systems containing these polyelectrolytes and other soluble ionic materials, such as ionic salts and phosphonates. These soluble ionic materials typically interfere with the ability of conventional techniques to monitor the concentration of the polyacrylic acids in aqueous systems.
Water soluble polyacrylic acid, polymethacrylic acid, polymaleic acid, and copolymers formed from at least 50 weight percent of acrylic, methacrylic, or maleic acid and less than 50 weight percent of another copolymerizable monomer and mixtures thereof, referred to hereinafter generally as polyacrylic acids, are used commercially as scale inhibitors and dispersants in such aqueous systems as cooling towers, boilers, oil field production facilities, sea water evaporators, and detergents. These polymers interact with scale forming, inorganic salts formed by the reaction of hardness ions, such a calcium and magnesium, with anions such as carbonate, phosphate and sulfate. The polyacrylic acids function by interfering with the growth of the crystals of these salts (antiprecipitation), or by introducing a repulsive surface charge to the crystals retarding their agglomerating, settling and depositing on surfaces (dispersion), or by interfering with the structure of the crystal itself making the scale more easily fracturable and dispersable (crystal modification). In addition, these polymers are also useful for dispersing other suspended particulate matter, such as clay, in aqueous systems. Rohm and Haas Company's ACRYSOL.RTM. LMW polymers of polyacrylic acids and their corresponding sodium salts, having weight average molecular weights ranging from about 1,000 to about 4,500, are known to be effective scale inhibitors in aqueous system to inhibit common hardness ion salts. In addition, U.S. patent application Ser. No. 485,560 also relates to water soluble, low molecular weight copolymers of acrylic acid and methacrylic acid which are useful for scale inhibition in aqueous systems. Further, U.S. patent application Ser. No. 485,559 relates to a method of dispersing inorganic materials in aqueous systems using low molecular weight copolymers of acrylic acid and hydrophobic comonomers.
Other organic compounds, such as organophosphates and organophosphonates, are also commonly used as scale inhibitors in aqueous systems. One such group of organic phosphonate scale inhibitors are manufactured and sold by Monsanto Chemical Company under the trademark Dequest.RTM.. In addition, other ionic compounds, such as inorganic phosphates, may also be used in these aqueous systems to assist in retarding the corrosion of metal surfaces.
Presently there is no simple, fast, reproducible, and sensitive, low cost method for selectively determining the concentration of polyacrylic acids in aqueous systems containing other soluble ionic materials such as hardness ions and phosphonates. The presence of these soluble ionic materials in the aqueous system interferes with the ability of conventional methods to measure small concentrations of polyacrylic acids, on the order of about 5 ppm or less, in such aqueous systems. One such technique in which soluble ionic salts interfere with the determination of the concentration of polyacrylic acids involves precipitation with bivalent copper, filtration, redissolution of the precipitate, and assay of unreacted bivalent copper (U.S. Pat. No. 3,516,795).
A suitable method for determining the concentration of polyacrylic acids in aqueous systems containing soluble ionic materials must be fast, simple, and capable of yielding reproducible results. It must avoid the use of toxic or hazardous chemicals, must be able to completely isolate polyacrylic acids from organic phosphonates, must be able to concentrate polyacrylic acids from the aqueous system to gain sensitivity, and must be capable of eliminating possible interference in the measurement caused by corrosion inhibitors, inorganic salts, colored impurities, and interspersed oil droplets.
Such a simple, fast, reproducible, and sensitive, low cost method for determining the concentration of polyacrylic acids in aqueous systems containing other soluble ionic materials is desired by operators of cooling towers, boilers, and other systems which use polyacrylic acids as scale inhibitors or dispersants. Such a monitoring method would allow operators to make economical decisions in the field concerning the timing and need for additional polyacrylic acids.
It is therefore an object of the present invention to provide a solution to the problem of monitoring the concentration of polyacrylic acids in aqueous systems by providing a simple, fast, reproducible, and sensitive, low cost method for selectively adsorbing and concentrating polyacrylic acids from aqueous systems containing other soluble ionic materials so that the concentration of the polyacrylic acids in the aqueous system can be determined.
It is also an object of the present invention to provide a method for quantitatively monitoring the concentration of polyacrylic acids in aqueous systems containing polyacrylic acids and other soluble ionic materials.
It is a further object of the invention to provide a method for determining the concentration of both polyacrylic acids and organic phosphonates in aqueous systems containing such compounds.